1. Field of the Invention
The present invention relates to a charged particle lithography apparatus, and in particular to an aperture array for a lithography system with a cooling system.
2. Description of the Related Art
Currently, most commercial lithography systems use a light beam and mask as a means to reproduce pattern data for exposing a target, such as a wafer with a coating of resist. In a maskless lithography system, beams of charged particles are used to write the pattern data onto the target. The beamlets are individually controlled, for example by individually switching them on and off, to generate the required pattern. For high resolution lithography systems designed to operate at a commercially acceptable throughput, the size, complexity, and cost of such systems becomes an obstacle.
Furthermore, existing charged particle beam technology is suitable for lithography systems for relatively course patterning of images, for example to achieve critical dimensions of 90 nm and higher. However, a growing need exists for improved performance. It is desired to achieve considerably smaller critical dimensions, for example 22 nm, while maintaining sufficient wafer throughput, e.g. between 10 and 100 wafers per hour. In order to achieve such a large throughput at ever decreasing feature sizes it is necessary to increase the number of beams generated by the system, increase the current in the charged particle beams, and reduce the distance between the beams.
The charged particle beams may be produced by collimating a single beam and generating multiple beams from the collimated beam using an aperture array having a plurality of apertures. The charged particle beams impinging on the aperture array will cause a significant heat load in the aperture array, and cause deformation of the aperture array. This deformation results in changing the dimensions of the aperture array due to expansion of the material from which the aperture array is constructed. This alters the spacing and alignment of the apertures which produce the separate charged particle beams, and unless corrected, will result in errors when writing the pattern onto the target.